1. Field of the Invention
The present invention relates to container assemblies. More particularly, this invention relates to various blast resistant and blast directing container assemblies for receiving explosive articles and preventing or minimizing damage in the event of an explosion. These container assemblies have utility as containment and transport devices for hazardous materials such as high explosives or a combination of high explosives plus shrapnel, e.g., grenades combined with pipe bombs. They are particularly useful in aircraft where weight is an important consideration, and more particularly in the cargo holds and passenger cabins of the aircraft. They are also particularly useful to bomb squad personnel in combating terrorist and other threats.
2. The Prior Art
In response to the 1988 terrorist bombing of a Pan American flight over Lockerbie, Scotland, experts in explosives and aircraft-survivability techniques have studied ways to make commercial airliners more resistant to terrorist bombs. One result of these studies has been the development and deployment of new generations of explosive detection devices. As a practical matter, however, there remains a threshold bomb size above which detection is relatively easy but below which an increasing fraction of bombs will go undetected. An undetected bomb likely would find its way into luggage either carried on board (in cabin) by a passenger or stored in an aircraft cargo container. Cargo containers, shaped as cubic boxes with a truncated edge, have typically been made of aluminum, which is lightweight but not explosion-proof As a consequence, there has been tremendous focus in recent years on redesigning containers to be both blast resistant to bombs that are below this threshold size and lightweight.
A good overview on redesigned aircraft cargo containers is found in Ashley, S., SAFETY IN THE SKY: Designing Bomb-Resistant Baggage Containers, Mechanical Engineering, v 114, n 6, June 1992, pp 81-86, hereby incorporated by reference. One type of container disclosed by this article is designed to suppress shock waves and contain exploding fragments while safely bleeding off or venting high pressure gases, while another type is designed to guide explosive products overboard by channeling blast forces out of and away from the airplane hull. Several of the new designs utilize composite materials that are both strong and lightweight. In one such design, a hardened luggage container is wrapped in a blanket woven from low density materials such as SPECTRA(copyright) fibers, commercially available from AlliedSignal Inc., and lined with a rigid polyurethane foam and perforated aluminum alloy sheet. A sandwich of this material covers four sides of the container in a seamless shell. In this regard, see also U.S. Pat. No. 5,267,665, hereby incorporated by reference.
Access to a container""s interior is necessary for loading and unloading and is typically provided by doors. Doors provide a significant weak point for the container during an explosion since a blast from within the container forces a typical door outward. If the door is connected through a hinge and metal pin arrangement, the pins become dangerous projectiles. If the door slides in grooves or channels, the grooves or channels may bend or distort to cause failure of the container. It would thus be desirable to have a container design that eliminates the aforesaid problems with doors for access to the container""s interior.
U.S. Pat. No. 5,312,182 discloses hardened cargo containers wherein the door engages by sliding in grooves/tracks with an interlock that ostensibly responds to such an explosive blast by gripping tighter to resist rupture of the device. The parent of this case, pending application Ser. No. 08/533,589, filed Sep. 25, 1995, addresses the door closure problem by utilizing at least three nested, mutually reinforcing, perpendicular bands of, preferably, a blast resistant material. Access to the interior of the container is provided by at least partially removing the two outer bands; this has not been found to be a user-friendly solution due to space constraints of the container on an aircraft or excessive handling of the container.
Other blast resistant and/or blast directing containers are described in European Patent Publication 0 572 965 A1 and in U.S. Pat. Nos. 5,376,426; 5,249,534; and 5,170,690. All of these publications are hereby incorporated by reference.
Containers for storing and/or transporting explosives such as bombs, or suspected explosives, are also known. See, for example, U.S. Pat. Nos. 5,225,622; 4,889,258; 4,432,285; 4,055,247; 4,027,601; and 3,786,956, all hereby incorporated by reference. These containers are typically made of a high strength outer housing having a fixed shape and containing a structure for supporting the explosive out of contact with the housing. High strength materials taught for forming the outer housing include metal, such as stainless steel or steel plate, and ballistic fiberglass. Supporting structures taught include vermiculite in a binder, foamed plastic (such as Styrofoam), foam rubber, and cardboard. The containers generally are heavy and have a bulky, fixed shape or construction.
The environment in which a container is to be used may have weight and space constraints, for example, the passenger cabin or cargo hold of an aircraft. Such constraints make desirable a collapsible container that folds into a compact shape for storage when not in use.
The present invention, which was developed to overcome the deficiencies of the prior art, provides blast resistant and blast directing containers and container assemblies, some of which are collapsible.
This invention is a blast resistant container assembly for receiving an explosive. The container assembly comprises a container having a band of blast resistant material covering an access opening. The band has at least one slit therethrough which can be aligned with a portion of the access opening for placing a suspected explosive inside the container. Blast mitigating material is optionally located within the container.
In another embodiment the blast resistant container assembly comprises at least three bands, one of which preferably comprises a blast resistant material. A first inner band is nested within a second band which is nested within a third band, with all bands being oriented relative to one another to substantially enclose a volume and to form a container wall having a thickness substantially equivalent to the sum of the thicknesses of at least two of the bands. Blast mitigating material is optionally located within the inner band.
In a particularly preferred embodiment the blast resistant container assembly comprises at least three seamless bands of a blast resistant material and an aqueous foam. One or more of the bands preferably is collapsible. The blast resistant material comprises high strength fibers having a tenacity of at least about 10 g/d and a tensile modulus of at least about 200 g/d. The bands are nested one within the other when assembled with their longitudinal axes at right angles to one another to substantially enclose a volume and to form a container wall having a thickness substantially equivalent to the sum of the thicknesses of at least two of the bands. The inner band preferably includes a foldable flap forming a lip on each side thereof and is stabilized to prevent twisting. The inner band can be stabilized by consolidation if it comprises a composite material or by affixing rigid plates or other support structure thereto if not susceptible to consolidation. The aqueous foam located within the inner band preferably has a density in the range of from about 0.01 to about 0.10 g/cm3, more preferably in the range of from about 0.03 to about 0.08 g/cm3, and preferably is inhibited from contact with the suspected explosive if used for bomb removal. This embodiment is particularly useful as an aircraft in-cabin emergency containment system or as a bomb squad container for transport and/or removal of bombs.
In an alternate embodiment, the present invention is a blast resistant container assembly for receiving an explosive wherein the container assembly comprises a container having an access opening; blast mitigating material located within the container; and at least one band of a blast resistant material. The band slides over the container in a first direction to encircle the container and at least partially cover the access opening, and in a second direction to at least partially expose the access opening. The band or bands together preferably cover substantially all of the surface area of the access opening. This embodiment is particularly useful for the containment and removal of explosives found by detection or screening devices, for example, in airports.
The three band box design of the preferred container assembly of this invention has several advantages over containers of the prior art. It eliminates the need for an entry door since access can be achieved through a slit in either the middle or innermost band. This eliminates one of the weak points of the prior art containers: door and panel hinges with steel rods are no longer necessary and neither are door-channel interlock systems. Other modifications permit easy access to the container""s interior for loading and unloading in spite of limited exterior space constraints. The box is not impervious to explosive""s gas and allows controlled release of the gas through the slit or slits, which contributes to the design function. The box production is technology inexpensive and simple. The bands of the box can be made rigid or flexible as desired. If the bands of the box are made with flexible edges and rigid faces, then they can be collapsed for more efficient storage and transported as a set of three or more essentially flat parts (bands) for subsequent assembly and use with the blast mitigating material.
Blast mitigating materials can absorb heat energy from the blast by an increase in temperature, phase transition, e.g., vaporization of water. They may collapse and absorb energy by crushing and/or visco-elastic effects. Condensable gases (in foams) may condense under elevated pressure, thereby liberating heat of condensation to the aqueous phase. Condensable gases will cause a decrease in shock wave velocity and through condensation transmit heat energy. Kinetic energy can be imparted to all of these materials.
The use of aqueous foam with condensable gas as a foaming agent significantly lengthens the time of venting and reduces the hazard. As such, it is a preferred blast mitigating materials. In bomb squad containers, however, where it is important to preserve evidence, the foam should be kept out of contact with the suspected bomb. A bladder is an efficient way to achieve this.